To provide service to tankers, many marine terminals equip their berths with all-metal bunker arms on one or both sides of the bank of cargo transfer arms. These bunker arms are installed at the berth with the intent that bunkering of the vessel, i.e., loading with fuel to power the vessel, can be accomplished quickly, economically, and without inconvenience to the terminal or vessel. Experience indicates, however, that for various reasons bunkering operations with the bunker arms often are not effective and cause delays to the departure of the vessel. The specific reasons encountered for difficulty in bunkering vessels directly with all-metal bunker arms include poorly designed and poorly located bunker manifold connections.
On many tankers, the bunker manifold connection is weak because of the use of: cast iron material, too small a flange and pipe diameter, and excessive overhang of the manifold from its deck support. Past analyses show that the all-metal bunker arms frequently create overstress in such manifolds and, therefore, the bunker arms cannot be used without the risk of failing the bunker manifold or manifold flange.
In addition to being weak, many manifolds often are inaccessible because of the need to locate them away from deck obstructions or because of lack of forethought on the part of the designers. When this is the case, the all-metal bunker arm either cannot reach the manifold without interference or cannot service the bunker manifold safely because it's outside the envelope of the bunker arm. The arm's envelope is the volume in space representing the location of manifolds the arm can service without causing overstress in the arm or the manifold. Finally, vessel owners are reluctant to retrofit the vessels with stronger, accessible bunker manifolds because of the high costs involved.
Many attempts have been made by terminals to circumvent these bunker manifold problems, including:
1. Extending a string of long, heavy rubber dock hose from the piping at the berth platform to the ship's bunker manifold. Such long lengths of hose often cannot be properly supported or repositioned as the ship deck elevation changes with draft and tide. Consequently, the hose is subject to rupture from damage caused by kinking or pinching action against the dock or fenders. Stringing the hose also is time-consuming.
2. Carrying aboard the vessel a heavy bunkering saddle which contains a horizontal section of pipe flanged at each end. The saddle must be lashed to the vessel's deck in a location where the forward flange falls inside the bunker arm's envelope. Hose then must be strung on deck from the rear flange of the saddle to the bunker manifold. While less hose is involved than with the previous method, carrying the heavy saddle aboard and lashing it in place is time-consuming and awkward. Further, since the vessels are not normally designed for mounting a saddle, it raises the question whether the marine arm is provided with a safe and substantial support while connected to the saddle.
3. Carrying aboard a special tee piece that is bolted to the cargo manifold adjacent to the bunker manifold and then connecting the bunker arm to this tee piece. A hose is run from the side outlet of the tee to the bunker manifold. The disadvantage to this method is the effect of carrying aboard the tee piece and the generation of higher stresses in the cargo manifold because of the increased overhang equivalent to the body length of the tee piece. The body length can be substantial because the bunker arm is usually made in a smaller diameter than the cargo manifold, making a long reducer section necessary.
4. Relocating the vessel at the conclusion of cargo transfer operations from its original berth to another berth with better bunker facilities. The practice of relocating the vessel can cause a substantial debit in turnaround time and berth occupancy rate.
Thus it is apparent that there still exists a need for a bunkering device that will accomplish quick, economical and convenient bunkering of vessels at conventional marine berths.